Modeling the Feasibility of Reducing Chloride Concentrations in an Urban Lake due to Road Salt Runoff

Salt pollution has become prominent over the past 80 years in freshwater ecosystems across the Midwest United States. This study focuses on chloride dynamics in Lake Wingra, a shallow, urban lake in Madison, Wisconsin. Since the 1940s, chloride concentrations have risen 30-fold to over 100 mg L⁻¹. While still below the chronic chloride water quality threshold of 230 mg L⁻¹, local stakeholders have a set goal of reducing concentrations to 40 mg L⁻¹. Here we investigate the interplay of precipitation and road salt application in driving observed chloride dynamics in the lake using a dynamic model. We then use the model to project future chloride concentrations under a range of road salt reduction scenarios. We find that under current road salt application rates, mean chloride concentrations in Lake Wingra will stabilize between 116 and 168 mg L⁻¹. Under a 75% salt reduction scenario, chloride concentrations will decrease to 42 mg/L by the 2050s.